Hi Doug,
Thanks... Presumably I'd just leave each possible pair of groups at a time in the qdec table, and delete rows corresponding to subjects of the remaining group? And then do stats on, e.g. "long.thickness-rate" to compare rate of change between the current pair of groups? Doesn't variability across all 3 groups somehow have to be accounted for?
Tudor
On 16 June 2014 20:38, Douglas Greve greve@nmr.mgh.harvard.edu wrote:
Yes, you could do each separately. doug
On 6/16/14 8:10 PM, Tudor Popescu wrote:
Dear FS list,
I have a data set with 3 groups (2 treatments, 1 control), each with equally-spaced time-points (pre and post structural scan). I've done the 3 longitudinal pre-processing steps, and stage#1 of the two-stage model, and I would prefer to run stage#2 (cross-sectional analysis of the difference) with QDEC as opposed to with mri_glmfit.
I know that QDEC is meant for 2 groups, but I see that designs with 4 or 6 groups can be analysed with QDEC (as per this https://surfer.nmr.mgh.harvard.edu/fswiki/FsgdExamples FSGD examples page) whereas designs with 3 groups cannot be. It seems to me that an even number of groups is QDEC-able while an odd number isn't, but is there any workaround so that I can still use QDEC? Perhaps if I only do pairwise comparisons one at a time, i.e. treatment1 vs control and treatment2 vs control?
Many thanks! Tudor
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